In the art of chilling liquids, it has long been common practice to provide metal cold plates having flow passages extending through them to conduct liquids to be cooled. The cold plates have surfaces that are contacted by a cooling medium, such as ice, to cool the plates and thereby cool the liquids conducted through them.
Ordinary or conventional cold plates are characterized by bodies of cast aluminum having flat horizontal upwardly disposed top icing surfaces, horizontally disposed bottom surfaces, and vertical side and end surfaces about and between the top and bottom surfaces. The cold plates include one or more elongate liquid-conducting tubes that are arranged within and formed to extend throughout the horizontal planes of the plates. The tubes have inlet and outlet end portions that project freely outwardly from sides of the plates where they are conveniently accessible to effect connecting them with related liquid-handling equipment.
The liquid-conducting tubes conduct potable liquids and are commonly formed of stainless steel tube stock.
Cold plates of the class referred to above and here concerned with are ordinarily placed in the bottoms of thermally insulated ice cabinets or chests, with means to allow for connecting the free ends of the tubes with related fluid-handling apparatus and in which blocks or cubes of ice are deposited to engage the top icing surfaces of the plates. The plates are formed or are disposed within the cabinets or chests to suitably drain water (ice melt) so that the ice might best remain in contact with the plates and is not subject to floating in water above the plates.
The usual method of making cold plates of the class here concerned with includes; first, forming lengths of stainless steel tubing with inlet and outlet portions and with serpentine intermediate heat transfer portions that are to extend throughout the central portions of the cold plates of which they are to be a part; second, arranging the formed tubes within split molds (of cast steel or the like) having spaced front and rear walls to define the top icing surfaces and bottom surfaces of cold plates and having perimeter walls to define the perimeter surfaces of the plates (the molds have openings or ports therein through which the end portions of the tubes freely project); and finally, pouring molten aluminum into the molds to cast the desired aluminum body about the tubes and to form the cold plates.
After the newly cast cold plates and molds have cooled sufficiently, the molds are opened and the plates are removed therefrom in accordance with common practices. Subsequent to the foregoing, the newly cast cold plates are suitably cleaned and dressed as circumstances require.
In practice, it is desirable that the rate at which liquids to be chilled move into through and from the cold plates be slowed to assure ample time to effect desired heat transfer between the liquids and the aluminum bodies of the plates. It is also desired that the wall thickness of the heat transfer tubes be maintained as thin as is practical and that they present as much surface area between the aluminum and the liquid to be chilled as is practical. To the above end, it has become common practice to provide cold plates with elongate tubing units having elongate inlet and outlet tube sections at their opposite ends and pairs of elongate parallel, smaller in diameter, intermediate heat transfer tube sections extending between and suitably connected with the inlet and outlet tube sections. The ends of the pairs of heat transfer tube sections and their related inlet and outlet tube sections are typically connected together by means of female Y-couplings into which the related ends of the tube sections are slidably engaged. The tube stock from which the pairs of heat transfer tube sections are made is typically smaller in diameter and has a thinner wall thickness than the tube stock from which the inlet and outlet tube sections are made. However, the combined flow capacity and surface area of the two small diameter tube sections is greater than the flow capacity and surface area of the larger diameter and heavier tubing of which the end sections of the units are made. Thus, the flow of liquid through the central or intermediate portions of the tubing units is effectively slowed, the surface area thereof is increased and the wall thickness thereof is effectively minimized.
Next, it is common practice to make cold plates of the character referred to above so that they cool several different liquids. For example, cold plates are commonly provided for use in beverage dispensing apparatus that function to deliver several different flavors of chilled beverages. In such cases, the cold plates are provided with and include, several (two, three, four or more) liquid-conducting tubing units of the character described above. Each of the units in such plates is utilized to conduct and effect chilling of one flavor of beverage. In such plates, the several tubing units are alike and are stacked together, one atop the other, and, during manufacture, are positioned in molds so that they will occur between and in spaced relationship below and above the top icing surfaces and the bottom surfaces of the plates. The central heat transfer tubing sections of the adjacent tubing units in such plates would preferably be arranged in contact with each other to effect heat transfer between the tubes and the liquids flowing therethrough and thereby achieve substantial uniform chilling of the several liquid beverages. To relate adjacent tubing sections in such a manner has been sought to be attained by others in the past but they attained such poor results such efforts have not been pursued.
The wall thickness of the Y-couplings provided to connect the end tube sections to the pairs of intermediate tube sections of tubing units of the character referred to above is greater than the wall thickness of the tubing stock from which the tube sections of the units are established. The diametric extent of each tubing unit is greater where the Y-fittings occur and the thickness or vertical extent of a stack of like tubing unit is substantially greater where the stacked Y-coupling occur than where the stack small diameter heat transfer tubes occur.
The vertical extent or thickness of the plates must be sufficiently great to freely and adequately accommodate the thickest portions of the stacked tubing units, where the stacked Y-couplings occur and are of greater thickness than is necessary where the stacked central heat transfer tubes of the units occur. Accordingly, when multiplicities of stacked tubing units are arranged in molds, preparatory to pouring molten aluminum about them to establish cold plates; and the end portions of the stacked units are properly oriented and held in desired position within the molds, the intermediate portions of those stacked units are suspended freely in the molds and are free to move about therein. When molten aluminum (at 1400.degree. F.) is poured into the molds and progressively flows into contact with the stacked tubing units, the thermal shock to which the stacked units are subjected causes the freely suspended portions of the tubes to expand, warp and twist in an erratic and uncontrollable manner.
As a result of the above-noted expanding, warping and twisting of tubes during pouring of the aluminum, the relative positioning of the tubing units within the finished cold plates is seldom, if ever, what the makers of the plates desire and is often what can be best described as a somewhat random array of tubing. As a result of such random array of tubing, the resulting cold plates are such that the spaces between and masses of aluminum about and between different parts of the tubing within the plates varies materially and randomly. As a result of the foregoing, the thermal conducting characteristics of such cold plates is neither uniform or predictable. One plate of a single production run of like plates might perform quite effectively and efficiently throughout its entire extent, while another might perform extremely ineffectively and inefficiently throughout its entire extent; while the performance of the remainder of the plates produced falls between those two extremes.
The prior art has long recognized that the heat exchange tubing in cold plates of the character here concerned with should not lie immediately adjacent to or become exposed at the top icing surfaces of the plates and have resorted to the use of various spacer devices and/or means to keep those tubes from moving too close to the walls of the molds that form the icing surfaces of the plates, during casting thereof. While those spacer means have served to prevent the tubes in such plates from being too close to the icing surfaces of the plates, they have not served to prevent the tubes from moving too far away from the walls of the molds that form the icing surfaces of the plates, during casting thereof, and have not worked to hold the adjacent portions of the heat transfer tubing sections of stacked tubing units in stacked engagement with each other. Accordingly, while the spacer means provided by the prior art prevent the heat conducting tube sections from moving too close to the icing surfaces of cold plates, they do not work to prevent those tube sections from moving too far from the icing surfaces and do not prevent thermal shocked-induced: movement of those tubes in any direction within the molds other than toward the icing surfaces forming walls of the molds. Thus, positioning of the heat transfer sections of stacked tubing units in prior art cold plates of the class here concerned with is somewhat random and is seldom, if ever, uniform.
The shortcomings and inconsistencies in the performance of cold plates provided by the prior art caused by displacement of the tubes therein as a result of thermal shock has become accepted in the art as an inherent shortcoming of such plates that cannot be overcome without considerable difficulty and an attending unacceptable increase in the costs exacted for such plates.